1. Field of the Invention
The present invention relates to a light quantity adjusting apparatus. More particularly, but not exclusively, the present invention relates to a plural blade diaphragm light quantity adjusting apparatus.
2. Description of the Related Art
With the recent miniaturization of image pickup apparatuses (e.g., video and still cameras), imaging optical systems, for example those mounted on image pickup apparatuses, have also been miniaturized. Often the miniaturization of the imaging optical system leads to miniaturization of any lens units in the imaging optical system. Alight quantity adjusting apparatus is often associated with these systems and is used to control light into the lens unit. Thus, as the lens unit is miniaturized so also is the light quantity adjusting apparatus.
For example, Japanese Patent Laid-Open No. 6-175194 discusses a conventional light quantity adjusting apparatus for use in an image pickup apparatus, such as a still camera and a video camera. This apparatus comprises plural diaphragm blades, each of which has a rotation shaft and an operating shaft, and also comprises a diaphragm ring that has cam grooves and a central opening. This apparatus engages the operating shaft of each of the plural diaphragm blades with a corresponding one of the cam grooves and also rotates the diaphragm ring to thereby simultaneously operate the diaphragm blades.
Japanese Patent Laid-Open No. 6-95204 discusses another conventional light quantity adjusting apparatus. This apparatus dispenses with the diaphragm ring and is configured so that each of plural diaphragm blades includes a cam groove and a cam groove engaging pin, and that the cam groove engaging pin of each diaphragm blade is slidably engaged with the cam groove of an adjacent diaphragm blade. The plural diaphragm blades are sequentially driven by a driving force transmitted from a drive member to each diaphragm blade.
Japanese Patent Laid-Open No. 2000-155352 discusses another conventional light quantity adjusting apparatus. This apparatus is configured so that an ND (Neutral Density) filter is bonded to each of a part of diaphragm blades, as used in a video camera which incorporates a CCD (Charge-Coupled Device) image sensor, and that when the diameter of a diaphragm aperture, defined by the diaphragm blades, is equal to or less than a predetermined value, the ND filter is inserted into the diaphragm aperture. When the diameter of the diaphragm aperture is reduced too much, thus an image sensor used in an image pickup section becomes relatively small, diffraction can adversely affect a picked-up image. Therefore, this apparatus employs the ND filter to thereby eliminate necessity for decreasing the diameter of the diaphragm aperture to be less than the predetermined value.
In a case where the plural blades are operated together by the diaphragm ring, backlash can be caused between the drive source and the diaphragm ring and between the diaphragm ring and each of the blades. Also, a loss in transmitting a driving force can increase due to friction generated in the cam grooves of the diaphragm ring. In the apparatus adapted to operate the sequentially connected diaphragm blades, backlash between engaging portions of the adjacent blades can be accumulated. Thus, it is difficult to enhance the accuracy of the diameter of the diaphragm aperture.
Also, the light quantity adjusting apparatus having the ND filter uses a dedicated power supply so as to control the ND filter independently. Consequently, the size of this apparatus increases.
Thus, there has been proposed an apparatus adapted to cause the diaphragm ring to operate a blade, which includes the ND filter, similarly to diaphragm blades. However, backlash between the diaphragm ring and the blade, which includes the ND filter, increases. Also, the loss in transmitting a driving force increases due to friction generated in the cam grooves.
Naturally, the use of the diaphragm ring increases the thickness of the entire apparatus.
Generally, many apparatuses are configured to drive two diaphragm blades and an ND filter through a seesaw type drive lever, which are used as a light quantity adjusting apparatus mounted on a video camera. The drive lever is driven by an electromagnetic actuator (or motor) serving as a drive source. There are two types of the ND filter. One type is stuck to one of the diaphragm blades by an adhesive agent. The other type serves as an independent separate member and is driven by a dedicated drive member. A light quantity adjusting apparatus having an ND filter of the latter type, as disclosed in Japanese Patent Laid-Open No. 2004-138953, is described with reference to FIG. 8.
FIG. 8 illustrates an exploded perspective view of a conventional light quantity adjusting apparatus 30.
In FIG. 8, reference numeral 32 designates a bottom board (that is, a casing) which includes a fixed opening 32f through which light passes. Reference numerals 35 and 36 denote diaphragm blades serving as light shielding members for shielding light, which can pass through the fixed opening 32f. Reference numeral 31 designates a rotary electromagnetic actuator (or motor) for driving the diaphragm blades 35 and 36 through a seesaw type diaphragm drive lever 33. Reference numeral 37 denotes an ND blade to which an ND filter 37a is stuck. Reference numeral 34 designates an ND drive lever for driving the ND blade 37.
The ND drive lever 34 has a laterally elongated hole 34a that engages with a projection 33a of the diaphragm drive lever 33, and also has an upwardly and downwardly elongated hole 34b that engages with projections 32d and 32e formed on the bottom board 32. Each of the diaphragm blades 35 and 36 has a corresponding one of laterally elongated holes 35a and 36a, which respectively engage with projections 33a and 33b formed on the diaphragm drive lever 33, and also has a corresponding one of upwardly and downwardly elongated holes 35b and 36b, which respectively engage with projections 32a and 32b formed on the bottom board 32. The ND blade 37 has a hole 37b, which is fitted onto a projection 32c of the bottom board 32, and also has an elongated hole 37c that engages with a projection 34c of the ND drive lever 34.
With this configuration, the diaphragm blades 35 and 36 are guided to the projections 32a and 32b of the bottom board 32, respectively, in response to a rotation of the diaphragm drive lever 33 driven by the motor 31. Then, the diaphragm blades 35 and 36 perform reciprocating motions in upward and downward directions of the light quantity adjusting apparatus 30, as viewed in this figure. Consequently, the diaphragm blades 35 and 36 move up and down in the region of the fixed opening 32f formed in the bottom board 32, to thereby substantially change the size of the fixed opening 32f. Thus, a quantity of light passing through the fixed opening 32f can be changed. In this apparatus of the aforementioned configuration, the ND drive lever 34 is guided by the projections 32d and 32e of the bottom board 32 in response to a rotation of the diaphragm lever 33 driven by the motor 31. Then, the ND drive lever 34 performs reciprocating motions in the upward and downward directions of the light quantity adjusting apparatus 30, so that the ND blade 37 rotates around the projection 32c of the bottom board 32.
That is, the two diaphragm blades 35 and 36 and the ND blade 37 are driven by a single drive source (the motor 31).
Other conventional light quantity adjusting apparatuses, each of which has four blades as disclosed in Japanese Patent Laid-Open Nos. 11-119296 and 2001-42382, are described hereinbelow by referring to FIGS. 9A and 9B, and FIGS. 10A and 10B.
FIGS. 9A and 9B illustrate explanatory views of another conventional light quantity apparatus 40. FIG. 9A illustrates an exploded perspective view of the apparatus 40. FIG. 9B illustrates a plan view of the apparatus 40 in a shutter closed state in which a case cover is removed.
In FIGS. 9A and 9B, reference numeral 41 designates a case serving as a supporting member. Reference numeral 42 denotes a case cover. Reference numerals 43, 44, 45, and 46 designate four sectors turnable in an opening and closing directions, that is, a first main blade (43), a first auxiliary blade (44), a second main blade (45), and a second auxiliary blade (46), respectively, in this order. Reference numeral 47 denotes a drive lever having a drive pin 47a. In the shutter closed state shown in FIG. 9B, each of the blades is held by a projection 42g, which is provided on the turn locus of the main blade 45 of the case cover 42, and a projection 41g, which is provided on the turn locus of the main blade 45 of the case 41, in a state in which the gap between the adjacent blades is more even and small. Consequently, a favorable light shielded condition is achieved. In the driving interval from the shutter closed state to a shutter opened state, the main blades 43 and 45 are released from the projections 42g and 41g, respectively, so that a drive load is reduced. This enables smooth opening and closing of a shutter.
FIGS. 10A and 10B illustrate explanatory views of another conventional light quantity apparatus 50. FIG. 10A illustrates an exploded perspective view of the apparatus 50. FIG. 10B illustrates a plan view of the apparatus 50 in an initial closed state.
In FIGS. 10A and 10B, reference numeral 51 designates shutter blades. The apparatus 50 has two outer blades 51a and 51d and two inner blades 51b and 51c. Reference numeral 59 denotes a photoreflector for detecting the positions of the shutter blades 51.
The outer blades 51a and 51b differ in turn-direction from the inner blades 51b and 51c. These shutter blades 51 are placed in such a way as to differ in the center of turn from one another. A slit is provided in an end part of each of the outer blade 51d and the inner blade 51c. In the initial state shown in FIG. 10B, in which the shutter blade 51d is closed, sensor light traveling between a light transmitting section and a light receiving section of the photoreflector 59 is blocked by the end parts of the shutter blades 51d and 51c. Abnormality is detected before exposure when the sensor light of the photoreflector 59 momentarily passes through the slit before the corresponding blade reaches a position, at which a flux of imaging light starts passing therethrough, while the shutter blades 51 move in the opening directions.
As described above, with reference to FIGS. 9A, 9B, 10A, and 10B, each of the conventional light quantity adjusting apparatuses 40 and 50 has the four blades and drives these blades (e.g., by using one drive source) so that the blades rotate around axes of rotation thereof, respectively. Incidentally, in each of the light quantity adjusting apparatuses 40 and 50, the number of the diaphragm blades is set to be larger than that of the diaphragm blades of the light quantity adjusting apparatus 30. Also, the size of each of the blades is decreased to thereby reduce the projected area thereof.
However, the conventional light quantity adjusting apparatus 30 shown in FIG. 8 uses a dedicated drive lever 34 so as to drive the ND blade 37. Thus, the number of components increases, so that the cost of the apparatus increases. Also, the thickness in the direction of an optical axis of the apparatus is increased by ensuring a space for the drive lever 34.
In the conventional light quantity adjusting apparatus 40 shown in FIGS. 9A and 9B, the first and second main blades 43 and 45 respectively turn ahead of the first and second auxiliary blades 44 and 46 during the transition from the closed state to the opened state. Thus, this apparatus cannot provide to the first and second auxiliary blades 44 and 46 functions that are other than a light shielding function, for example, a function of alleviating image deterioration due to the diffraction of light, which is caused in the case of the small diaphragm aperture.
The conventional light quantity adjusting apparatus 50 shown in FIGS. 10A and 10B cannot realize a completely closed state unless all the four shutter blades 51, that is, the outer blades 51a and 51d and the inner blades 51b and 51c are used. Consequently, this apparatus cannot provide to the shutter blades 51 functions that are other than the light shielding function and that are, for example, the function of alleviating image deterioration due to the diffraction caused in the case of the small diaphragm aperture.